U.S. patent number 5,452,296 [Application Number 08/151,794] was granted by the patent office on 1995-09-19 for asynchronous transfer mode communication system.
This patent grant is currently assigned to NEC Corporation. Invention is credited to Hiroshi Shimizu.
United States Patent |
5,452,296 |
Shimizu |
September 19, 1995 |
Asynchronous transfer mode communication system
Abstract
An ATM communication system capable of minimizing the delay
period and achieving high throughput without requiring setting of
the corresponding virtual connection (VC) table and routing. The
communication system includes a vacant virtual connection table
indicating unused VC. The VC is retrieved in response to a
transmission demand and set in an ATM cell as a virtual connection
ID (VCI). Then, the cell is transmitted with added address
information identifying the destination. An ATM switch and a
routing controller determine routing from a transmitting terminal
to a receiving terminal. The determined routing is stored in a
routing table in the routing controller. Then, through the
determined routing, data is transferred from the transmitting
terminal to the receiving terminal.
Inventors: |
Shimizu; Hiroshi (Tokyo,
JP) |
Assignee: |
NEC Corporation
(JP)
|
Family
ID: |
18196838 |
Appl.
No.: |
08/151,794 |
Filed: |
November 12, 1993 |
Foreign Application Priority Data
|
|
|
|
|
Nov 12, 1992 [JP] |
|
|
4-327235 |
|
Current U.S.
Class: |
370/399 |
Current CPC
Class: |
H04L
49/254 (20130101); H04L 49/3081 (20130101); H04L
49/602 (20130101); H04Q 11/0478 (20130101); H04L
49/3009 (20130101); H04L 49/552 (20130101); H04L
2012/5632 (20130101); H04L 2012/5667 (20130101) |
Current International
Class: |
H04Q
11/04 (20060101); H04L 12/56 (20060101); H04J
003/02 () |
Field of
Search: |
;370/60,60.1,94.1,93,92,91,58.1,58.2,58.3,54,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
CCITT. Study Group XI/Working Party XI/6 Qetion: 20/XI, 22-26 Jun.
1992..
|
Primary Examiner: Olms; Douglas W.
Assistant Examiner: Vu; Huy D.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen
Claims
What is claimed is:
1. A communication system performing an asynchronous transfer mode
(ATM) communication employing fixed length cells, comprising:
an ATM switching circuit having a plurality of input ports and a
plurality of output ports and providing a virtual connection
mutually connecting an input port and an output port;
a routing control means for controlling said ATM switching circuit
to form a virtual connection corresponding to a virtual connection
identification and a destination address set in transmitting cells
applied to the input port;
a plurality of transmitting terminals for transmitting the cells
respectively coupled to said input ports;
a plurality of receiving terminals for receiving the cells from one
of the transmitting terminals respectively coupled to said output
ports;
each of said transmitting terminals including:
a vacant virtual connection table for storing virtual connections
presently unused in said ATM switching circuit;
retrieving means for retrieving an unused virtual connection from
said vacant virtual connection table in response to a transmission
demand for transmitting the cells from the transmitting terminal to
one of the receiving terminals;
and transmitting means for setting the retrieved virtual connection
as said virtual connection identification of said transmitting
cells in each transmitting cell, and setting the destination
address and a calling party address for specifying the transmitting
terminal in a leading cell of the transmitting cells;
wherein said routing control means comprises:
management table means, including a management table, for
registering the virtual connection identification, the destination
address and the calling party address set in the leading cell
received at the input port in said management table;
and controlling means for switching said ATM switching circuit to
form the virtual connection corresponding to the virtual connection
identification and destination address set in the leading cell.
2. A communication system as set forth in claim 1, wherein second
and subsequent cells except for said leading cell are directly
transferred from an input port to an output port without passing
through said routing control means.
3. A communication system as set forth in claim 2, wherein the
receiving terminal connected to said output port receives the
transmitted cells from said output port.
4. A communication system as set forth in claim 3, wherein each of
said transmitting terminals further includes a table for
establishing correspondence between said destination address and
the virtual connection of said destination address.
5. A communication system as set forth in claim 4, wherein each of
said receiving terminals further includes a table for establishing
correspondence between said calling party address and the virtual
connection of said calling party address.
6. A communication system as set forth in claim 2, wherein each of
said transmitting terminals further includes transmitting means for
transmitting only the leading cell to said routing control means at
every given interval, and said management table means of said
routing control means registers the virtual connection
identification, the destination address and the calling party
address set in said leading cell received at said every given
interval.
7. A communication system as set forth in claim 2, wherein each of
said transmitting terminals further includes transmitting means for
transmitting only the leading cell to said routing control means
when the transmitting cells are not transmitted to said ATM
switching circuit within a given period.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention setting of virtual connection (VC) in an
asynchronous transfer mode (ATM) communication system. More
specifically, the invention relates to a VC setting system for a
local area network (LAN) communication.
2. Description of the Related Art
An ATM communication system employing a fixed length cell as a
transfer unit has an excellent characteristics permitting uniting
point-to-multipoint communications and multi-media communications.
Therefore, in recent years, the ATM communication system is
attracting attention in the application for LAN communication.
Here, in burst communication, original information, i.e. service
data unit (variable length) is transmitted by dividing into fixed
length cells including 5 octets of header and 48 octets of payload,
as shown in FIG. 8. Routing in the ATM system is performed using a
virtual connection ID (VCI) in the header.
In an ATM communication system, there are two VC setting systems,
i.e. a method for setting the VC employing a dedicated VC for
signaling setting and a permanent virtual connection (PVC) for
semi-permanently setting the VC.
The former method employs a similar method to call setting in an
integrated service digital network (ISDN), namely, C
(control)-plane and U (User)-plane are set separately and the call
in U-plane communication is set by C-plane, which method is
referred to as "outband signaling".
On the other hand, the later method does not employ C-plane, in
which routes for all distant users are preliminarily established
for selecting VC depending upon the distant user to call.
The PVC method has been disclosed in Japanese Unexamined Patent
Publications Nos. 2-234538, 1-144745, 1-126043, 2-239749, 2-284543
and 3-97334.
In the former method employing outband signaling, the following
drawback can be encountered. Namely, the communication in C-plane
is a communication not with the distant user but with a call
control portion. In case of communication between users with small
data amount, the data amount to be handled by U-plane becomes
substantially equal to the data amount to be handled by C-plane to
cause large overhead resulting in increasing of the delay period
and degradation of throughput.
On the other band, in the later technology, namely the method to
preliminarily set routes for all distant users, a defect is
encountered in the limitation of capacity for setting depending
upon bit length of VC. For instance, in case of 16 bits VC, the
maximum number of routes is limited at approximately 64000.
In addition, the later PVC method has a shortcoming that a routing
table for defining correspondence between VCI and address
information has to be preliminarily prepared upon establishing the
system. Furthermore, preparation of the routing table requires
complicated operation and possibly causes error.
SUMMARY OF THE INVENTION
The present invention is to resolve the defects and drawbacks in
the prior art as set forth above. Therefore, it is an object of the
present invention to provide an ATM communication system which
permits high speed communication and has high flexibility and
expandability.
Another object of the invention is to provide an ATM communication
system which can reduce required operation in establishing the
system.
In order to accomplish the above-mentioned and other objects, a
communication system performing an asynchronous transfer mode
communication employing a fixed length cell, comprises:
a vacant virtual connection table indicating a value of unused
virtual connection;
retrieving means for retrieving the value of the unused virtual
connection from the vacant virtual connectiontable in response to a
transmission demand; and
transmitting means for setting the retrieved value of the virtual
connection as a virtual connection identification of the cell and
performing transmission with adding address information specifying
destination to the cell.
The communication system may further comprise:
a switching system including means for determining routing from the
transmitting means to the destination on the basis of the address
information and a routing table for storing the determined routing;
and
receiving means for receiving data from the transmitting means
through the routing determined by the switching system.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the
detailed description given herebelow and from the accompanying
drawings of the preferred embodiment of the invention, which,
however, should not be taken to be limiting of the invention but
are for explanation and understanding only.
In the drawings:
FIG. 1 is a block diagram showing the construction of the preferred
embodiment of an ATM communication system according to the present
invention;
FIGS. 2(a).about.2(c) are conceptual diagrammatic illustrations
showing examples of registration of a vacant VCI table 11, a VCI-IP
address table 12, a routing table 31 and VCI-IP address table
41;
FIGS. 3(a) and 3(b) comprise an illustration showing a format of an
ATM cell to be employed in the preferred embodiment of the ATM
communication system of the invention;
FIGS. 4a and 4b is a conceptual illustration showing an example of
transfer of ATM cell of a service data unit in the ATM
communication system of FIG. 1;
FIGS. 5(a) and 5(b) are block diagrams respectively showing
constructions of a transmitting terminal and a receiving terminal
in FIG. 1;
FIG. 6 is a block diagram showing an example of an internal
structure of an ATM switch and a routing controller in FIG. 1;
FIGS. 7(a).about.7(c) are conceptual illustrations showing another
registration method of the IP address; and
FIG. 8 is a conceptual illustration showing a typical transfer
method for the service data unit employing the ATM cell.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention will be discussed
hereinafter with reference to the accompanying drawings. FIG. 1 is
a block diagram showing a construction of one embodiment of an ATM
communication system in accordance with the present invention. The
shown embodiment of the ATM communication system includes an ATM
switching system (ATM system) comprising a transmitting terminal 1
as a transmitting device, an ATM switch 2 and a routing controller
3, and a receiving terminal 4 as a receiver device.
In the shown embodiment, the ATM switch 2 has four ports
PN1.about.PN4 at an input port side (IN side) and four ports
PN1.about.PN4 at an output port side (OUT side). The ATM switch 2
is controlled by the routing controller 3 for establishing routing
connection between respective inlet ports and outlet ports.
It should be appreciated that other transmitting terminals and
receiving terminals other than the transmitting terminal 1 and the
receiving terminal 4, are connected to respective ports of the ATM
switch 2. In the transmitting terminal 1, a vacant VCI table 11,
and a VCI-IP (internet protocol) address table 12 are provided. On
the other hand, in the receiving terminal 4, a VCI-IP address table
41 is provided. Also, in the routing controller 3, a routing table
31 is provided. Detailed discussion will be given later.
In the shown embodiment, the following discussion will be given in
connection with a communication from the transmitting terminal 1
connected to the port PN2 at the input port side to the receiver
terminal 43 connected to the port PN4 at the output port side.
At first, the internal structures of respective components in FIG.
1 will be discussed. Initially, the internal structures and
operations of the transmitting terminal 1 and the receiving
terminal 4 are discussed with reference to FIGS. 5(a) and 5(b).
FIG. 5(a) is a block diagram showing an example of the internal
structure of the transmitting terminal 1, in which the transmitting
terminal 1 includes a buffer 15 for temporarily storing data to be
transmitted, i.e. a service data unit (SDU), a cell assembling
means 14 for dividing the data stored in the buffer 15 and
assembling fixed length cells. The transmitting terminal 1 further
includes a processor 13 for adding VCI or AD for the header
portions of respective cells after assembling the cells, the vacant
VCI table 11 indicating VCs currently not used, and the VCI-IP
address table 12 indicating correspondence between the currently
used VC and the IP address of distant user on communication.
With the construction set forth above, the service data unit stored
in the buffer 15 is supplied to the cell assembling means 14 and
thus divided into the fixed length cells. Then, the processor 13
reads out the IP address and sets an identification bit AD of the
cell containing the read out IP address. Also, the processor 13
makes reference to the VCI-IP address table 12 on the basis of the
read out IP address of the distant terminal to make a call. When
the IP address has already been registered in the table 12, the
corresponding VCI is written in the headers of respective cells. On
the other hand, if the IP address is not registered, a vacant VC,
i.e. the VC which is not currently used, is selected from the
vacant VCI table 11 to register in the VCI-IP table 12. Thereafter,
the VCI is written in the headers of respective cells. Each cell is
supplied to the input port of the ATM switch in order.
Here, in the foregoing operation, further discussion will be given
for variation of content of registration of the vacant VCI table 11
and the VCI-IP address table 12 when the read out IP address has
not been registered in the VCI-IP address table 12. FIG. 2(a) is a
conceptual diagrammatic illustration showing an example of
variation of the content of registration of the vacant VCI table 11
and the VCI-IP address table 12.
In FIG. 2(a), "2" and "3" are registered in the upper side vacant
VCI table 11, and correspondence between VCI "1" and IP address
"110" and correspondence between VCI "5" and IP address "013" are
registered in the VCI-IP address table 12. When the processor 13
makes reference to the vacant VCI table 11, the VCI "2" which is
currently not used can be selected. Then, the VCI "2" can be
corresponded to an IP address "123" of the distant receiver
terminal 4 and registered in the VCI-IP address table 12.
The lower side of FIG. 2(a) shows the vacant VCI table 11 and the
VCI-IP address table 12 after modification. As can be seen, the
correspondence between VCI "2" and the IP address "123" is
registered. By this, the VCI "2" becomes occupied state and thus
eliminated from the vacant VCI table 11. Therefore, in the vacant
VCI table 11, only VCI "3" remains.
On the other hand, FIG. 5(b) shows the internal structure of the
receiving terminal 4. In FIG. 5(b), the receiving terminal 4
includes a cell disassembling means 44 for disassembling the cells
and restoring the service data unit, a buffer 45, the VCI-IP
address table 41 indicating the correspondence between the received
IP address of the transmission side terminal and the VCI, and a
processor 43 for performing the writing process for the table
41.
In the construction set forth above, the cells supplied from the
output port of the ATM switch are input to the cell disassembling
means 44. Then, the payload portion of respective cells are fed to
the buffer 45 in order and accumulated therein. By this, the
original service data unit can be restored by interconnecting the
payloads accumulated in the buffer 45. In conjunction therewith,
the processor 43 reads out the IP address from the cell and writes
the correspondence between the read out IP address and the VCI in
the VCI-IP address table 41 for registration.
When the read out IP address has not been registered in the VCI-IP
address table 41, the VCI-IP address table 41 is updated in the
manner as illustratively discussed hereinafter. FIG. 2(b) is a
conceptual illustration showing an example of variation of the
content of registration in the VCI-IP address table 41.
In the upper side VCI-IP address table 41 in FIG. 2(b), the
correspondence between VCI "3" and the IP address "101", and the
correspondence between VCI "2" and the IP address "211" are stored.
Here, by communication from the transmitting terminal via the ATM
switch, new correspondence between the VCI and the IP address is
registered in the VCI-I address table 41. The lower table in FIG.
2(b) shows addition of the correspondence between VCI "1" and the
IP address "210" of the transmitting terminal 1.
Next, the internal structure and the operation of the ATM switch
and the routing controller will be discussed. FIG. 6 is a block
diagram showing the internal structure of the ATM switch 2 and the
routing controller 3 in FIG. 1, in which the like reference
numerals represent like elements.
In FIG. 6, the ATM switch 2 comprises input buffers 21 and 22
provided corresponding to respective input ports, output buffers 23
and 24 provided corresponding to respective output ports and a
switching circuit 20 forming connection switches between respective
input and output buffers. On the other hand, the routing controller
3 includes the routing table 31 for registering correspondence
between the input port and the output port of the ATM switch 2, a
read/write control circuit 32 for identification of the output port
and assigning VCI at the output port according to the content of
registration in the routing table 31, and a processor 33 for
determining the output port on the basis of the IP address of the
distant terminal to be called and select the vacant VCI at the
output port for registering in the routing table 31.
With the construction set forth above, the input buffer stores the
data from the transmitting terminal 1 per cell. Then, the
read/write control circuit 32 reads out the VCI of the cell in the
input buffer and performs identification of the output port and
assignment of the VCI at the output port according to the content
of registration in the routing table 31 (later-mentioned path 3) in
FIG. 1).
When registration is not found in the routing table 31, the fact is
recognized by the processor 33. Then, the processor 33 determines
the output port on the basis of the IP address of the distant
terminal to be called and selects one of the vacant VCI at the
output port to register as the VCI (later-mentioned paths 1 and 2
of FIG. 1).
From the output buffer, respective cells are supplied to the
receiving terminal 4 after assigning the VCI corresponding to the
output port.
Discussion will now be given for variation of the content of
registration in the routing table 31 when the registration is not
found. FIG. 2(c) shows an example of variation of the content of
registration.
In the left side of routing table 31 in FIG. 2(c), there are
registrations indicating the facts that "PN1" and VCI "4" of the
input port (IN) correspond to "PN3" and VCI "2" of the output port
(OUT); and "PN3" and VCI "1" of the input port correspond to "PN1"
and VCI "6" of the output port. Here, by communication from the
transmitting terminal, additional registration is made for the fact
that "PN2" and VCI "2" of the input port corresponds to "PN4" and
VCI "2" of the output port. This is illustrated in the right side
routing table 31 in FIG. 2(c).
As set forth, the transmitting terminal 1 is provided with the
function of dividing the data to be transmitted, i.e. a packet
frame or service data unit (SDU) into one or more ATM cells. FIG. 4
diagrammatically shows the manner of dividing of the data and
assembling the cells to be performed by the transmitting terminal
1. Namely, in FIG. 4, assuming that the original service data unit
consists of an SDU header (header portion) and an SDU payload
(information portion), the transmitting terminal 1 performs a
process of dividing the service data unit into a plurality of cells
and adds the distant user address, such as the IP address of the
distant user, to the headers of the cells, as shown in FIG. 4(a).
Then, among a plurality of ATM cells, a process is performed for
setting (AD=1) the identification bit AD for the cell containing
the IP address.
Here, as shown by the hatched area in FIG. 3, the identification AD
may be defined in 5 octets of cell header in the cell format (FIG.
3(a)), or, in the alternative, may be defined in the payload header
in the 48 octets cell (FIG. 3(b)). For the cells not including the
IP address, the identification bit AD will not be set (AD=0).
It should be noted that, in FIGS. 3(a) and 3(b), GFC represents a
general flow control, VPI represents a virtual path ID, the VCI
represents the virtual connection ID, HEC represents a header error
control.
Returning to FIG. 4, each cell assigned VCI "2" (FIG. 4(a)) is
input to the input port PN2 of the ATM switch 2. In the ATM switch
2, the header portion is re-written and output to the output port
PN4 as the cell assigned VCI "1" as shown in FIG. 4(b). The cells
thus output to the output port PN4 is transmitted to the receiving
terminal 4.
It should be appreciated that the SDU header of the service data
unit contains the IP address consisted of a calling party IP
address indicative of the transmitting terminal and a destination
IP address indicative of the receiving terminal. Routing are
determined on the basis of these addresses.
Returning to FIG. 1, in the communication system constructed as set
forth above, the transmitting terminal 1 initially searches the
vacant VCI table 11 to obtain the vacant VCI=2 at the occurrence of
SDU for which the VC is not set. Then, the pair of the VCI "2" and
the IP address "123" of the receiving terminal 4 are written in the
VCI-IP address table 12. Second and subsequent cells are also
assembled as VCI=2 as shown in FIG. 4(a). However, since the second
and subsequent cells do not contain the IP address information, the
identification bit AD thereof are set to zero.
At the input port PN2 of the ATM switch 2, since the route for the
VCI=2 is not yet set, the non-routed cells are connected to the
routing controller 3 (1 of FIG. 1). The routing controller 3 then
checks the destination IP address to select the output port PN4 and
assigns the vacant VCI=1 (2 of FIG. 1). Subsequently, by the
routing table 31, for the VCI=2 of the input port PN2, the VCI=1 of
the output port PN4 is assigned. Therefore, the cell arrives at the
receiver terminal 4 as cell of VCI=1. The second and subsequent
cells are directly transferred from the input port PN2 to the
output port PN4 without passing through the routing controller 3
since the path has already been set in the routing table 31 (3 of
FIG. 1).
The receiving terminal 4 registers the VC=1 as new VC in its own
VCI-IP address table. It should be appreciated that the IP address
information is set as the SDU header with not only the destination
IP address, i.e. the IP address "123" of the receiving terminal 4
but also the address "210" indicating the transmitting terminal 1.
Therefore, as shown in FIG. 2(b), the VCI-IP address table 41 in
the receiving terminal 4 is consists of the correspondence of the
IP address of the transmitting terminal 1 and the VCI. The VCI-IP
address table may be expanded to include correspondence between the
VCI, the IP address of the calling party and the destination IP
address, Also, the routing table 31 in the routing controller 3,
not only the correspondence between the PN numbers of the input and
output ports and the VCI, the calling party IP address and the
destination IP address may be stored.
When the set VC is maintained without elimination, the leading cell
of the service data unit having AD=1 can pass the path illustrated
by 3 of FIG. 1.
In the foregoing description, when the VC is not set, only cell of
AD=1 passes the path of 1.fwdarw.2 of FIG. 1 and other cells pass
the path 3. However, it is possible to perform the process per a
variable length service data unit as shown in FIG. 4 for updating
the routing table when the VC is not set. Namely, at the input port
PN2, when the cell, for which the VC is not yet set, arrives, the
cells are supplied to the routing controller 3 irrespective of
whether AD=1 or not. Then, an ATM adaptation process is performed
by the routing controller 3 to restore the variable length service
data unit, to determine the route and to assign the VCI on the
basis of the IP address information contained in the header of the
service data unit. In this case, all cells forming the first
service data unit pass the path of 1.fwdarw.2 of FIG. 1.
It should be appreciated that although the foregoing embodiment
performs setting of VC upon transfer of the service data unit, it
is possible to define the IP address transferring cell
independently of transfer of the service data unit. This method is
illustrated in FIG. 7.
Namely, as shown in FIG. 7(c), by setting "1" for the
identification bit AD of the cell header portion, the IP address
transferring cell is identified. Then, independently of data
transfer, IP address pair (destination IP address and calling party
IP address) is transferred for setting the VC.
Here, in order to transfer the IP address pair independently of the
data transfer, transmitting timing becomes important. As shown in
FIG. 7(a), the IP address pair may be transmitted at every given
interval T.sub.0. Alternatively, as shown in FIG. 7(b), the IP
address pair may be transmitted when a period where no data is
transmitted, exceeds a given period T.sub.1. It should be noted
that, in FIGS. 7(a) and 7(b), arrows represent IP address pair
transferring cells and hatched portions represent normal data
transferring periods on the normal cell base.
In addition, various methods may be employed in canceling the set
VCI or for restoring the past set VCI. Namely, the VCI may be
canceled per service data unit when absence of cell transmission is
maintained for a predetermined period of time. On the other hand,
the VCI may be restored by means of a special cell or so forth.
The address information should not be specified to the IP address,
but can be known ISDN address, MAC (media access control) address,
or any other address information which can specify the terminal or
host.
As set forth above, according to the present invention, without
employing the outband signaling, switching of the VC can be
realized. Therefore, the ATM communication system with minimized
delay period and high throughput can be realized.
Also, in contrast to PVC, since the corresponding table of the VC
and the routing is not required to input upon establishing of the
system, complicated operation is not required. Also, the system can
be operated with minimized occurrence of error. Furthermore, the
ATM communication system thus constructed has high
expandability.
Although the invention has been illustrated and described with
respect to an exemplary embodiment thereof, it should be understood
by those skilled in the art that the foregoing and various other
changes, omissions and additions may be made therein and thereto,
without departing from the spirit and scope of the present
invention. Therefore, the present invention should not be
understood as limited to the specific embodiment set out above but
should include all possible embodiments which can be encompassed
within the scope of the claims and equivalents thereof.
* * * * *